1. Field of the Invention
The present invention relates to a vacuum pump in which the temperature of a stator becomes higher than the temperature of a rotor.
2. Description of the Related Art
Conventionally, there has been used a vacuum pump such as a turbo-molecular pump for chamber evacuation in a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus, or the like. In recent years, in an etching process performed by a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus, an increase in the amount of reaction products adhered to a vacuum pump has been causing problems such as an increase of troubles of contact between a rotor of the vacuum pump and reaction products and requirement of an overhaul within a short period of time after starting the operation of the apparatus. Thus, there has been a need to make the temperature inside the pump (the temperature of a gas contact part) considerably higher than a conventional temperature to suppress adhesion of reaction products.
A method as disclosed in JP 09-072293 A is known as a method of increasing the temperature inside a pump. In the technique disclosed in JP 09-072293 A, a heating target member which is arranged to face the outer periphery of a rotor is directly heated.
However, in JP 09-072293 A, one end of a heating unit is fixed to the heating target member, and the other end thereof is fixed to abase. Thus, when the heating target member expands by heating, the expansion of the heating target member is disturbed in a part of the heating target member to which the end of the heating unit is fixed, and an unnatural stress is generated in the heating target member. Further, the temperature of the rotor also increases along with an increase in the temperature of the heating target member. Thus, the rotor thermally expands toward the outer peripheral side (toward the heating target member). On the other hand, since the thermal expansion of the heating target member toward the outer peripheral side is disturbed in the part to which the end of the heating unit is fixed, a gap between the rotor and the heating target member becomes smaller, which may cause contact between the rotor and the heating target member.